Cutting large gears a economically satisfactory rates involves very heavy chip loads which, in turn, impose heavy forces on various elements of the cutting machine structure. In particular, the cutting chip loads impose intermittent torsional loads of heavy magnitude on the generating train which provides the timed driving connection between the oscillation of the machine's cutter-supporting cradle and the rotation of its workpiece-supporting work spindle. Since these loads vary in magnitude and occur intermittently as each cutting blade of the cutter abruptly engages and disengages the cut, intermittent winding and unwinding of the generating train is induced due to the backlash in the several gear meshes within the train and the torsional resilience of the connecting shafts. This wind-unwind action is not only reflected by the cutting blade in the cut, causing chatter, poor cutter life, and unacceptable surface finish in the rough cut parts, but it also imposes high stresses on the elements of the generating train.
It has heretofore been common to use cradle and work spindle brakes and other similar apparatus to reduce the adverse effects of the very heavy chip loads involved. However, when cutting gears of large diameter and coarse pitch, such solutions are only satisfactory if the rate of infeed of the tool is slowed to keep chip loads relatively light, thereby resulting in low production rates. Heretofore, such large gears have generally been cut with planing generators in which the cutting tool strokes through the tooth slot being cut in an essentially linear path. Such machines are relatively slow and attempts to increase their production rates have been thwarted by their inability to cut large gears and tooth slots of acceptable quality at higher speeds.